Uniform Strains and Deformation Potentials

Abstract

A perturbation method of calculating the energy levels of a crystal modified by an arbitrary uniform strain is studied. A modified form of first-order perturbation theory is used, a form particularly appropriate to cases where the unperturbed wave functions are expanded in terms of orthogonalized plane waves. Not only are the conventional uniform strains considered but also the special types of deformations whereby the relative positions of the atoms in a unit cell are changed without distorting the Bravais lattice of the crystal. Thus the results of this paper may be applied to the deformation-potential theory of mobility with regard to both acoustic and optical lattice vibrations.